The present invention relates to an electronic device and to a method for fabricating the same. More particularly, it relates to wire forming technology.
With the recent trend toward higher integration of an integrated circuit, a wire-to-wire spacing has been reduced so that an electrical parasitic capacitance occurring between wires has been increased. However, the electrical parasitic capacitance between wires should be reduced in the integrated circuit of which a high-speed operation is required.
To reduce the electrical parasitic capacitance between wires, a method which reduces the relative dielectric constant of an insulating film formed between wires (hereinafter referred to as an inter-wire insulating film) is used at present. As a conventional inter-wire insulating film, a silicon oxide film (with a relative dielectric constant of 3.9 to 4.2) has been used frequently. In some integrated circuits, a fluorine-containing silicon oxide film (with a relative dielectric constant of 3.5 to 3.8) lower in relative dielectric constant than the conventional silicon oxide film has been used as an inter-wire insulating film. There has also been proposed a method which uses a carbon-containing silicon oxide film as an inter-wire insulating film as a method for maximally reducing the electrical parasitic capacitance between wires.
In the carbon-containing silicon oxide film, carbon exists in the form of an alkyl group or a phenyl group having a large volume. This reduces the density (1.0 to 1.3 g/cm3) of the carbon-containing silicon oxide film to a value lower than the density (2.3 g/cm3) of a silicon oxide film and also reduces the relative dielectric constant (about 2.0 to 3.0) of the carbon-containing silicon oxide film to a value lower than the relative dielectric constant (3.9 to 4.3) of the silicon oxide film. For example, a relative dielectric constant of about 2.8 can be achieved with a carbon-containing silicon oxide film having a density of about 1.3 g/cm3 and an in-film carbon concentration of about 20 at %.
FIG. 8 is a view showing a wiring structure in a conventional electronic device using a carbon-containing silicon oxide film as an inter-wire insulating film (see Japanese Laid-Open Patent Publication No. HEI 11-87503 (Paragraph Nos. 0015 to 0034)).
As shown in FIG. 8, lower-layer metal wires 4 each composed of a first tantalum nitride film 2 and a first copper film 3 are formed in a first insulating film 1 composed of a silicon oxide film formed on a silicon substrate (not shown). A second insulating film 5 composed of a silicon carbide film is formed over the lower-layer metal wires 4 and the first insulating film 1. A third insulating film 6 composed of a carbon-containing silicon oxide film is formed on the second insulating film 5. The third insulating film 6 has a damaged layer 6a formed by reforming a surface portion of the third insulating film 6. A fourth insulating film 7 is formed on the third insulating film 6. A via hole 8 reaching the lower-layer metal wire 4 and wiring grooves 9 for upper-layer wires are formed in each of the third and fourth insulating films 6 and 7. A plug 12 composed of a second tantalum nitride film 10 and a second copper film 11 is formed in the via hole 8. An upper-layer metal wire 13 composed also of the second tantalum nitride film 10 and the second copper film 11 is formed in each of the wiring grooves 9.
However, the foregoing conventional electronic device has the problem of e.g., a defective wiring structure, specifically the problem that the upper-layer metal wires 13 are not formed in connected relation to the plug 12, i.e., the problem that the wiring grooves 9 are not formed in connected relation to the via hole 8.